The prior art, such as for example U.S. Pat. No. 3,673,954, reveals that it has been common practice to apply decorations of one type or another to the exterior of glass containers such as for example bottles and drinking tumblers. The containers are decorated by the well known silk screen process wherein a moving array of containers is moved toward the decoration station by means of a conveyor. The containers are then positioned in a holding jig or fixture. The container is then printed while being subjected to rotation about its axis of symmetry. The actual printing is achieved by means of a silk screen that carries thereon the design that is to be imparted to the exterior sidewall of the container.
One or more colors have been applied to the exterior of a glass container. Such decoration has in the past necessitated a release of the container from the holding fixture and a transfer back to the conveyor where the container is moved to another decoration station. Thus, in the past, the application of four or five colors required the same number of printing stations and also the same number of container handling operations.
Also, it is well known to utilize the silk screen technique for reproducing color photographs on flat surfaces. Such photographic reproduction has been quite acceptable, particularly when organic inks have been used.
The use of organic, as well as inorganic coloring pigments, have been silk screened onto the exterior of glass containers, however, such decorations generally rely upon a composition where the colors actually overlay each other or are positioned adjacent each other.
The prior art also sets forth another decorative process known as halftone printing. In this process the various colors within a color original are separated and halftone positives are then made. In order to create a full complement of colors and hues, at least three halftone positives are necessary; each one representing one of the primary colors, such as for example magenta, cyan and yellow. The halftone positives are then placed on a silk screen to create images on the silk screen. By subjecting the container to three or more passes of the primary color halftone negatives, a composite picture is created. Throughout the entire operation precise alignment must be held so that the color dots fall adjacent each other.
Accordingly, it is an object of the present invention to provide a novel method for the printing of opaque glass enamels by the halftone process.
Another object of the present invention is to obtain an array of colors and hues heretofore not obtainable by the halftone process of printing on glass with opaque glass enamels.
A further object of this invention is to create a decorated glass article with the use of a plurality of primary colors deposited through a halftone screen.
Another object of the invention is to so vary the angles of the halftone dots so as to eliminate the moire effect.
An additional object of the present invention is to vary the percentage of the pigment in the opaque glass enamels so as to produce hues and colors not obtainable by mixing the pigments themselves.
It is another object of the present invention to produce colors approaching magenta red without the incorporation of gold into the glass enamel formulation.